show tooltip for artifacts in the header bar

src/lib/config/ConfigLoader.cpp

@@ -279,6 +279,12 @@ WorldConfig ConfigLoader::loadWorld(const std::string& path)
         cfg.buildingBlocksTooltip = *tip;
     }
 
+    if (const std::optional<std::string> tip =
+            tbl["world"]["artifact_tooltip"].value<std::string>())
+    {
+        cfg.artifactTooltip = *tip;
+    }
+
     cfg.regions.asteroidWidth_tiles     = static_cast<int>(requireInt(tbl["regions"]["asteroid_width_tiles"],      file, "regions.asteroid_width_tiles"));
     cfg.regions.playerBufferWidth_tiles = static_cast<int>(requireInt(tbl["regions"]["player_buffer_width_tiles"], file, "regions.player_buffer_width_tiles"));
     cfg.regions.contestZoneWidth_tiles  = static_cast<int>(requireInt(tbl["regions"]["contest_zone_width_tiles"],  file, "regions.contest_zone_width_tiles"));

src/lib/config/WorldConfig.h

@@ -82,6 +82,10 @@ struct WorldConfig
     // (REQ-UI-BLOCKS-TOOLTIP). Presentation-only; the simulation ignores it.
     std::optional<std::string> buildingBlocksTooltip;
 
+    // Optional hover-tooltip for the header artifact count display
+    // (REQ-UI-ARTIFACTS-TOOLTIP). Presentation-only; the simulation ignores it.
+    std::optional<std::string> artifactTooltip;
+
     WorldRegions regions;
     WorldExpansion expansion;
     WorldPush push;

src/test/ConfigLoaderTest.cpp

@@ -88,6 +88,11 @@ TEST_CASE("ConfigLoader loads the committed bin/config/ configs end-to-end", "[c
     REQUIRE(*cfg.world.buildingBlocksTooltip ==
             "Spend building blocks to build; deliver them to the HQ to gain more.");
 
+    // Optional header artifact tooltip (REQ-UI-ARTIFACTS-TOOLTIP).
+    REQUIRE(cfg.world.artifactTooltip.has_value());
+    REQUIRE(*cfg.world.artifactTooltip ==
+            "Choose the artifact reward when destroying enemy stations; collect enough to win.");
+
     // Spot-check that a config-derived formula computes as expected.
     // threat_rate_formula = "x": evaluates to the input value.
     REQUIRE(cfg.world.waves.threatRateFormula.evaluate(1.0) == Approx(1.0));

src/ui/HeaderBar.cpp

@@ -32,6 +32,11 @@ HeaderBar::HeaderBar(const GameConfig* config, QWidget* parent)
             QString::fromStdString(*config->world.buildingBlocksTooltip));
     }
     m_artifactsLabel = new QLabel(tr("Artifacts: 0/?"), this);
+    if (config->world.artifactTooltip)
+    {
+        m_artifactsLabel->setToolTip(
+            QString::fromStdString(*config->world.artifactTooltip));
+    }
     m_bossLabel      = new QLabel(tr("Boss Wave #1  Next boss: 5:00"), this);
     layout->addWidget(m_timeLabel);
     layout->addWidget(m_blocksLabel);